The striking increase of uterine blood flow during pregnancy is essential both for optimal growth of the fetus and cardiovascular well-being of the mother. Maladaptation of the uteroplacental circulation during gestation is associated with high incidence of clinical complications including preeclampsia and fetal development abnormality. Large-conductance Ca2+-activated K+ (BKCa) channels play a critical role in regulating uterine blood flow in pregnancy. Recent studies in sheep demonstrated that pregnancy and steroid hormones caused a significant increase in BKCa ?1 subunit resulting in increased ?1:? subunit stoichiometry and heightened BKCa channel activity in uterine arteries. Yet the molecular mechanisms remain unknown. Our preliminary studies showed that pregnancy and steroid hormones caused a decrease in DNA methylation at the ?1 gene promoter. DNA methylation is a chief mechanism in epigenetic repression of gene expression patterns. Recent studies suggest a robust mechanism of ten-eleven translocation 1-3 (TET1-3) proteins in active DNA demethylation. Preliminary studies suggested that pregnancy and steroid hormones increased TET1-2 expression in uterine arteries. These findings lead to the proposed studies of a highly novel mechanism testing the hypothesis that steroid hormone-mediated dynamic changes of DNA methylation and demethylation play a key role in regulating expression and function of BKCa channels in uterine vascular adaptation to pregnancy. Two specific aims will determine whether: 1) steroid hormone-mediated promoter demethylation and BKCa ?1 gene up- regulation play a causal role in increased BKCa channel function in uterine arteries in pregnancy, and 2) steroid hormone-mediated up-regulation of TET1-3 plays a causal role in active DNA demethylation and the ?1 gene up-regulation in pregnancy. The proposed study presents a major breakthrough and paradigm-shifting focus of research aiming at unraveling highly novel epigenetic mechanisms of hormone-mediated DNA demethylation in regulating gene expression patterns in uterine vasculature in particular, and in vascular smooth muscle function in general. The outcome of the proposed study will significantly advance our knowledge in molecular mechanisms of uteroplacental adaptation to pregnancy and improve our understanding of pathophysiological mechanisms underlying maladaptation of uteroplacental circulation and pregnancy complications. Because of the vital importance of BKCa channel function in regulating vascular tone and pressure in virtually all vascular beds, and the extremely limited knowledge in epigenetic regulation of BKCa channel expression and activity in vascular smooth muscle, the proposed study will indeed have a much broad impact in comprehensive understanding of molecular mechanisms in regulating BKCa channel activity and vascular function in physiology and pathophysiology.